In order to maintain adequate blood pressure in critical care patients, crystalloid or colloid solutions must be infused at a fast rate. It is also essential that the rate of infusion is not so high as to produce a circulatory overload. The adequacy of infusion is best judged by the hydrostatic pressure in the vein into which the fluids are infused. The patient also needs to be given medications which at times cannot be mixed in the infusion bottle because of incompatibility. Such medications are injected from a syringe through a separate lumen and released at a different site in the vein for immediate dilution by the blood stream. It is also necessary to obtain samples of the patient's blood from time to time to make diagnoses or to gauge the patient's progress. The triple-lumen catheter of the present invention is intended to be tailored to the specific requirements of such patients.
Numerous critical-care catheters are already known, but they have various disadvantages.
Howes U.S. Pat. No. Re. 31,873 describes a triple-lumen catheter with a transversely cut tip and intended to be introduced through a hypodermic needle. The catheter contains three identical tubes enclosed into a circular tube that forms the body of the catheter. The longest lumen opens at the end of the catheter while the other two lumens open at staggered locations. Another embodiment uses a cylindrical tube trisected by three radial septa into three identical lumens so that all the lumens can be used interchangeably for the intended functions. Commercial catheters similar to those described in the Howes patent have one of the lumen slightly larger than the other two, but large areas of dead space between the lumens makes this catheter relatively inefficient.
Howes U.S. Pat. No. 4,894,057 describes a triple-lumen catheter of construction similar to the above and containing three circular lumens of equal size for use interchangeably, or with one lumen slightly larger than the other two. Grooves are formed on the surface of the catheter extending from the exit port of each lumen to the end of the catheter to minimize the mixing of the fluid infused through the lumens. Traditionally the existence of grooves on catheter surfaces has been avoided because of the potential to form clots.
Another previously proposed triple-lumen catheter uses a circular tube that contains three radial septa arranged in a spiral form within the tube. Each lumen is therefore a spiral lumen, and the three lumens have identical cross sections. This spiral flow path offers a significant resistance to fluid flow.
Mahurkar U.S. Pat. No. 5,221,255 describes a triple-lumen catheter consisting of a circular tube divided into a semicircular lumen for fluid infusion in hypotensive patients, and two quarter-circle lumens for injection of fluids or obtaining samples of blood or measurement of hydrostatic pressure. This is the first example of a triple-lumen catheter for performing the critical functions discriminately. The septa contained in the circular tube form a "T" beam that makes the catheter kink resistant. The dead space wasted in the circular lumen catheter is also eliminated. This device satisfies the requirements of a triple-lumen critical care catheter, but the fluid flow efficiency is not as high as desired for many critical care applications.